We report findings concerning the relationship between electroencephalography (EEG) frequency during spike-and-wave discharges (SWDs) and response to treatment in 21 patients with idiopathic generalized epilepsy (IGE). We studied patients whose EEG contained SWDs lasting at least 4 s. Among these patients, two groups could be distinguished on the basis of a subtle difference in EEG frequency during the first 2 s of the burst. The two groups differed markedly in their clinical response to medication, with the group becoming seizure-free during the next 1-2 years showing a spike-wave onset frequency of >3.2 Hz, and those not seizure-free <3.2 Hz (p = 0.0034, sensitivity 75% and specificity 92%). Given this strong effect in a relatively small group, further work is needed to clarify the predictive value of this frequency measure for clinical outcomes in absence epilepsies.

Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom Institute of Psychiatry, King's College London, London, United Kingdom Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, United Kingdom Sheffield Institute for Translational Neuroscience, University of Sheffield, United Kingdom.